prompt-builder

prompt-builder is a skill for Claude Code from fabioc-aloha/Alex_Skill_Mall. It costs 18 tokens per session (1,281 once invoked), scanned A, original, MIT.

A guide to creating and checking .prompt.md files, which are Markdown files that define reusable prompts for an agent system.

In plain words
What is it for?
Use it when creating, fixing, reviewing, or registering prompts in a prompt-driven agent workflow.
Why use it?
Missing required frontmatter or an incorrectly structured prompt can make automated checks fail. It helps prompts meet the expected format.

Skill for Claude Code

Written for Claude Code: $ARGUMENTS substitution.

Good fit Use it when creating, fixing, reviewing, or registering prompts in a prompt-driven agent workflow.

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Install with agentmods
npx agentmods add skills/fabioc-aloha/alex_skill_mall/prompt-builder
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add fabioc-aloha/Alex_Skill_Mall --skill prompt-builder
Clone the repo
git clone --depth 1 https://github.com/fabioc-aloha/Alex_Skill_Mall

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for prompt-builder

README.md
[![agentmods](https://agentmods.dev/badge/skills/fabioc-aloha/alex_skill_mall/prompt-builder/github.svg)](https://agentmods.dev/skills/fabioc-aloha/alex_skill_mall/prompt-builder)
Your own site
<a href="https://agentmods.dev/skills/fabioc-aloha/alex_skill_mall/prompt-builder"><img src="https://agentmods.dev/badge/skills/fabioc-aloha/alex_skill_mall/prompt-builder/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for prompt-builder

Your own site · 80×15
<a href="https://agentmods.dev/skills/fabioc-aloha/alex_skill_mall/prompt-builder"><img src="https://agentmods.dev/badge/skills/fabioc-aloha/alex_skill_mall/prompt-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 18 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,281 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00018 $0.01281
Opus 5 $0.00009 $0.00641
Sonnet 5 $0.00004 $0.00256
Haiku 4.5 $0.00002 $0.00128

Measured 7d ago against content hash a66f52cec190, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

prompt-builder scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 7d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

plugins/ai-agents/prompt-builder/skills/prompt-builder/SKILL.md · 185 lines

How it starts

The opening of the file, as written. The whole thing — 185 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Prompt Builder

Build .prompt.md files that pass brain-qa on first attempt — no regressions


When to Use

  • Creating a new .prompt.md file
  • Fixing a failing prompt in brain-qa
  • Adding prompts to the loop menu config
  • Reviewing prompt frontmatter for completeness

Prompt Anatomy

Every .prompt.md has two parts: YAML frontmatter and Markdown body.

Frontmatter (Required Fields)

Field Required Gate Purpose
description Yes Yes What the prompt does (1 sentence)
application Yes Yes When/why to use it (distinct from description)
mode Conditional No Set to agent for loop prompts
agent Conditional No Named agent for root prompts
tools Conditional No Tool array for loop prompts

Gate fields (description + application) are mandatory — brain-qa fails without both.

brain-qa Scoring (4 points)

Flag Points Rule
desc 1 description: exists in frontmatter
app 1 application: exists in frontmatter
agent 1 agent: OR mode: agent exists
>20L 1 Body exceeds 20 lines

Pass = both gates (desc + app) AND score >= 3.


Two Archetypes

Root Prompts (.github/prompts/*.prompt.md)

Invoked directly by name. Typically route to a named agent.

---
description: "What this prompt does"
application: "When to use this prompt"
agent: the AI assistant
---

Key rules:

  • Use agent: to name the target agent (the AI assistant, Researcher, Validator, etc.)
  • Do NOT use mode: or tools: — those are for loop prompts
  • Body should be 20+ lines with clear instructions

Loop Prompts (.github/prompts/loop/*.prompt.md)

Sidebar buttons in the extension Loop tab. Loaded by loopMenu.ts.

---
mode: agent
description: "What this prompt does"
application: "When to use this prompt"
tools: ["read_file", "create_file", "run_in_terminal"]
---

Read the full file on GitHub · 185 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 7d ago First seen · 185 lines · 18 tokens per session scan A a66f52cec190

Subscribe to this mod's changes

prompt-builder is a skill published in the GitHub repository fabioc-aloha/Alex_Skill_Mall (4 stars, last pushed today), licensed MIT. It adds 18 tokens to every session and 1,281 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.